For wireless network systems, the path-loss between the transmitter and receiver is a critical factor that determines the possible range of communication between two nodes. Complex environments such as urban canyons and building interiors often contain numerous obstacles that impede the Line-Of-Sight (LOS) communication and increase the path-loss. The existing long range ad-hoc communication network relies on multi-path (multiple reflection, diffraction, and penetration through obstacles). In these environments especially at high frequencies the path-loss dramatically increases, which often requires higher transmitter power and closely spaced communication nodes. Furthermore, as transmitter power increases or as transmitting nodes become closer, the potential for mutual interference between communication cells increases which, if present, can cause degradation in coverage capacity. Additionally, a topology that uses closely spaced nodes will be more expensive than a similar topology sparsely populated with nodes. To overcome these situations and to help improve the ground area coverage of communication signals without increasing the transmitter power, radio repeaters have been extensively used in various application scenarios. Numerous studies regarding feasibility and operation of the radio repeater have been presented.
Additionally, numerous commercial products utilizing the concept of the radio repeater have been introduced and fabricated. The main objective of the radio repeater in these scenarios is to achieve enhanced connectivity by amplifying a radio signal through an active device as shown in FIG. 1. For the downlink communication, from a base station to an end-node/unit, the signal originating at the base station is linked through the receive antenna (RX) of repeater, amplified, and re-transmitted through the transmit antenna (TX), and vice versa for the uplink direction. However, the mutual coupling between a repeater's RX and TX antennas generates a positive feedback loop as shown in FIG. 1. When the gain of the RF amplifier is greater than the isolation level of the RX and TX antennas, the overall system will start to oscillate, and the communication coverage of that microcell cannot be established. Thus, the level of mutual coupling limits the performance of a radio repeater as well as the dimension and cost of the overall system.
To circumvent this intrinsic problem, generally two approaches have been proposed. The first method is to divide the frequencies of the uplink and downlink signals. This methodology utilizes Frequency Division Duplex (FDD) to reduce the mutual coupling by separating signal frequencies. However, it requires complex circuitry, larger size, and a common protocol to manage frequency allocation, which implies a higher cost and much more power consumption. The second method is to adapt the Time Division Duplex (TDD) in time domain. This also introduces additional logic circuitry, latency, and knowledge of the repeater, transmitter and receiver locations.
Therefore, it is desirable to develop an improved radio repeater designed to overcome the adverse effect of various complex environments by reducing the path-loss. This section provides background information related to the present disclosure which is not necessarily prior art.